The candidate has had a longstanding interest in understanding virus host interactions at a mechanistic level. His long-term professional goal is to pursue an academic research career studying the molecular biology that underlies the AIDS pandemic. As a post-doctoral fellow he was attracted to the area of HIV-1 assembly because the cell biology of this key process is still so poorly understood. The HIV-1 Gag protein is the only viral protein required for the production of virus like particles, however, recently it is becoming clear that numerous cellular factors must play essential roles in the process. The broad, long-term objective of this research proposal is to increase knowledge about virus-host interactions that are essential for HIV-1 assembly. The HIV-1 Gag protein is targeted to the site of virus assembly, the plasma membrane, through its amino terminal domain, MA. It is a complete mystery how MA directs assembly with high specificity to the plasma membrane. Important clues to this mystery are revealed from studies in murine cells, where plasma membrane targeting of HIV-1 Gag fails completely. Murine cells exhibit a dramatic block to the assembly of HIV-1. Preliminary studies have successfully produced Gag-chimeric HIV-1 that carry murine leukemia virus (MLV) MA in place of HIV-1 MA which we designate MHIV. MHIV chimeras are able to overcome this block to assembly. Further study of novel variants and mutants of MHIV will provide additional insights into how the HIV-1 MA protein functions in humans and why it malfunctions in mouse. This recent work supports a hypothesis that murine cells lack a key cofactor of MA that is needed to target assembly to the plasma membrane. In pursuit of this hypothesis, biochemical and molecular genetic experiments will exploit murine cells to identify human cDNAs that can complement the mouse deficiency. Preliminary studies show the feasibility of using HIV-1 cDNA libraries to identify positive regulators of HIV-1 production in mouse cells. These studies are designed to provide fundamental new insights into the mechanisms of assembly and may lead to novel strategies for therapeutic intervention of HIV-1 infection. In addition, chimeric virus studies may directly result in the production of viruses to be used in a mouse model for HIV-1 infection.